Desktop Pick-&-Place Machine: An EETimes Community Project

Would you be interested in having your own pick-and-place machine that can assemble your boards -- and possibly even reflow them -- while fitting in a space smaller than an 11" x 17"?

With all the excitement associated with of 3D printers, there seems to be a giant gap in the rapid prototyping tool set -- a desktop pick-and-place (P&P) machine that can be had at a reasonable price. If you were to survey the landscape, you would find that most of the smaller pick-and-place machines that are out there are either just not quite ready for primetime, or will cost more than a few thousand dollars. This is where the EETimes community has an opportunity to change the picture.

The idea started at this year's EELive! Conference and Exhibition. A few of us were standing around at one of the Gadget Smackdowns chatting about this and that. Among the various topics we discussed were the popularity of presentations on mechanical design and the need for a way to get reasonable prices on low-volume production/prototype runs. It was then that these two ideas converged and we decided that we wanted to design a very small pick-and-place machine.

The more we talked about this, the more excited we got. The thought of having a machine that can assemble your boards -- and possibly even reflow them -- while fitting in a space smaller than an 11" x 17" footprint just brought great big grins to our faces.

This idea -- with the excitement it brings -- is more than just designing a machine. There is a teaching opportunity as well. We will be using this project to teach concepts about electromechanical integration, motor usage, computer vision, PCB assembly, and a range of related topics through our blog posts and future conference presentations.

So what exactly will this machine consist of, and what tasks will it be capable of performing? Well, this is where we would appreciate your help. We do have some basic goals, but we would welcome your suggestions to fill out the details.

Let's start with out top-level design goals, which are as follows:

$400 to $600 target sales price

11" x 17" or smaller footprint

A modular system allowing for addition of features at a future date

Good mechanical design

With these as the basic design goals, here are some thoughts on other details to get your creative juices flowing. Because of the fact that we are shooting for a low price point, there will need to be some tradeoffs. For example, this is not intended to be the fastest pick-and-place machine out there, so we can look at compromising on speed.

Also, because we are not intending to use this machine to provide high throughput, we can look at eliminating the typical component feeders (though we may have a concept that could mitigate this tradeoff). Lastly, because we are looking to have a small machine, we are not intending to have an extremely large build area. Remember that this is intended to be a machine for very low volume production -- say a few hundred pieces, or prototypes.

There is an advantage to this being a small machine, which is that we can look at employing some concepts that might be too complex to implement on a production-level machine. For example, one concept we would like to consider is making this machine so that it cannot only print solder paste without stencils, but that it can then be able to reflow the entire board after the components have been placed. Another idea is to have a component tester. This concept would allow for testing of polarity of LEDs and other diodes. In turn, this would help insure less iterations of your concept due to mislabeled diodes.

So we have a basic framework and some design concepts to get the gears turning in your head. Now we need your help to gather ideas on what you would like to see in this type of a machine. We encourage you to share your comments below. After everyone has posted their ideas, we might use a poll tool to help narrow down some of these concepts. Once we have a better idea as to what the community would like to see in such a machine, there will be further chances to participate in this project. We look forward to seeing your creativity in action.

Regarding conductive epoxy, here's a repeat of a comment I made last year:

Around 1990 there was a promising attempt to use CNC technology to make circuit boards by Ariel Electronics (California). They created a gadget called the Circuit Writer which extruded conductive plastic wires onto a substrate, basically a 2-D plotter with an extrusion head. I actually visited Ariel and saw a Circuit Writer working. I don't think the technology got anywhere, but maybe it was just ahead of its time and with newer 3D extrusions this could be done practically. For more info, Google "ariel electronics circuit writer".

Your comments show much experience. Agreed - conductive polymers are not going to replace solder for every application.

Like so much of life... the devil is in the details.

Cost: I can get both solder and conductive polymers cheaper than what you quoted... and what ever it is today, will be different tomorrow. Often the difference is based on where you are.

Shelf life: similar observations to above (we don't like to keep solder for more than 6 months and never reuse by placing excess back into storage)

Curing: agree.. some curing heat is generally required. But much lower temps than solder. Especially the higher temps of ROHS solders.

Smearing: correct can be easier to be corrected when using solder. But always a bad situation. Even solder balls create problems.

Wicking (surface tension): this depends on the pcb surface finish. OSP (organic surface protectant) type finish, solder doesn't generally wet beyond where you put it. ENIG or HASL variations generally the solder will wet entire surface. And, yes , the surface tension can re-align a component with solder. Some designs and facilities depend on this characteristic of solder. But if often this creates as many problems as it solves (tomb stoning, floating off center because on thermal issues, solder balls floating around in the assembly). Better solution: just put the part where it belongs... and expect it to stay there. And don't bump it until it is cured or reflowed! I have seen articles by "experts" claiming the lack of wetting and automatic re-alignment with many new ROHS solders helps them reduce solder bridging! .. go figure...everyone seems to view this differently.

An item many have ignored: ROHS vs NON_ROHS compliance on components, specifically the surface finish of the connecting points. It is generally not recommended to mix soldering materials and component types. This is not an issue with conductive polymers.

You are correct .. conductive polymers are not appropriate for everything. But I was directing my thoughts to whom I thought would be using a table top machine with all the processing done at one station... for prototying or very small production runs.

Generally,

- Thermal conductivity:

Yep.. metal is better. But most applications don't approach the limits of either material.

- Resistance:

The differenences over 0.0005-0.001" thickness in the junction typically larger than 20 sq mil, are minor. Assuming use of quality conductive epoxy intended for this application. Unless you are sensitive to variations of less than 0.00001 ohms (you might be).. I don't think it will matter much. Many are not aware of the variations they may be experiencing with solder on current sense resistors. Good pcb layout methods are the primary concern for current sensing.

- Mechanical differences:

Many are not aware of the sensitivity of the some of the components to variations in connection process to the mechanical strength of the joints. Ceramic capacitors with high plate density (capactitance per volume) often demonstrate large deviations in quality due to this.

Example: the measured shear strength of a soldered X7R chip capacitor varies significantly with capacitance for a given size. I have measured a range of 2-17lbs for single location/size. While the same location/size with conductive epoxy showed very little standard deviation from 7 lbs of shear strength.

It was determined the capacitor's end platng (based on density) was the primary reason for the large std dev in the soldered joint performance. And the primary reason for this sensitivity to the quality of the capacitor end plating was exposure to higher temperatures and sensitivity to flux activation level (all mild).

Because of the physical space to work with and the minimum capacitance over temperature extremes and voltage required.... we had to work with capacitors that were (at the time) near the limits of how much capacitance we could get in a given volume (size).

I couldn't find a capacitor manufacturer that didn't display some form of this problem. I couldn't tolerate less than 5lbs shear strength on ANY product (avionics -55.+125C rating with high shock and vibration requirements). So, the ONLY solution at the time was to replace solder process with high temp rated conductive epoxy.

Connection junctions are typically a very small fraction of a square. (bulk resistance of a given material, generally specified in "squares" with a given thickness or resistance per cm)

Which is a very, very different animal compared to conductive epoxies vs copper used for traces (many squares) , often an issue when using bendable circuitry (copper vs conductive polymers).

I agree that DFN/QFN/QFP parts are a must. I think that BGA's could be accomodated, though I think that the biggest issue will be the overall size and weight of the package. I have given some initial thought into how to handle large (>100 pin QFP sized parts) packaged, though it is far from fully baked.

In the area of holding small PCB's, this is still very notional. I need to do some research on this. If you happen to have any links that might give some great solutions to small PCB holding, let me know and I will use them as research.

In some cases, stencils make a lot of sense, in other places, they do not. I for example will turn a handful of designs in a short time period, and the board itself only costs me $1-5 for three copies. The stencil will cost more than the board. In this case, I can save a significant amount by having this integrated into a machine that can print the paste.

On the other hand, if I were trying to do a few hundred boards, then the case you presented might argue for going the stencil route as you can do this faster, though it still will require more workspace.

In my opinion, making and using a stencil is too easy to try to automate the solder-paste dispensing in such a small machine. See, for example, http://imajeenyus.com/electronics/20100109_solder_stencil/index.shtml